The lithium ion battery is a secondary battery with a high energy density, and is used for a power source of portable devices such as a notebook computer and a mobile phone by taking advantage of its characteristics. There are various types in the shape of the lithium ion battery, and a wound-type structure of a positive electrode, a negative electrode, and a separator is adopted in a cylindrical lithium ion battery. For example, a positive electrode material and a negative electrode material are each applied to two sheets of belt-like metal foils, a separator is interposed therebetween, and a laminated body thus obtained is wound spirally, thereby forming a wound group. This wound group is housed in a cylindrical battery can used as a battery container, and is sealed after electrolytic solution is injected therein, so that a cylindrical lithium ion battery is formed.
Regarding the cylindrical lithium ion battery, a 18650 lithium ion battery has been widespread as a lithium ion battery for consumer use. An outer size of the 18650 lithium ion battery is as small as about 18 mm in diameter and about 65 mm in height. Lithium cobalt oxide characterized by a large capacity and long life is mainly used for a positive electrode active material of the 18650 lithium ion battery, and the battery capacity is approximately 1.0 Ah to 2.0 Ah (3.7 Wh to 7.4 Wh) in general.
In recent years, it is expected that the lithium ion battery is developed not only for the consumer use in portable devices and the like, but also for the use of large-scale energy storage system for natural power sources such as photovoltaic power generation and wind power generation. The large-scale energy storage systems require an amount of electric power per system in an order of magnitude of several megawatts/hour (MWh).
For example, Patent Document 1 listed below discloses a cylindrical lithium ion battery which includes, in a cylindrical battery container, an electrode wound group in which a positive electrode, a negative electrode, and a separator are wound. This battery has a discharge capacity of 30 Ah or larger, a positive electrode active material composite containing lithium manganese composite oxide is used for a positive electrode, and a negative electrode active material composite containing amorphous carbon is used for a negative electrode.